Deep dental phenotyping and a novel FAM20A variant in patients with amelogenesis imperfecta type IG

OBJECTIVES

To identify etiologic variants and perform deep dental phenotyping in patients with amelogenesis imperfecta (AI).

METHODS

Three patients of two unrelated families were evaluated. Genetic variants were investigated by exome and Sanger sequencing. An unerupted permanent third molar (AI1) from Patient1 and a deciduous first molar (AI2) from Patient2, along with three tooth-type matched controls for each were characterized.

RESULTS

All three patients harbored biallelic pathogenic variants in FAM20A, indicating AI1G. Of the four identified variants, one, c.1231C > T p.(Arg411Trp), was novel. Patient1 possessed the largest deletion, 7531 bp, ever identified in FAM20A. In addition to hypoplastic enamel, multiple impacted teeth, intrapulpal calcification, pericoronal radiolucencies, malocclusion, and periodontal infections were found in all three patients, gingival hyperplasia in Patient1 and Patient2, and alveolar bone exostosis in Patient3. Surface roughness was increased in AI1 but decreased in AI2. Decreased enamel mineral density, hardness, and elastic modulus were observed in AI1 enamel and dentin and AI2 dentin, along with decreased phosphorus, increased carbon, and increased calcium/phosphorus and carbon/oxygen ratios. Severely collapsed enamel rods and disorganized dentin-enamel junction were observed.

CONCLUSIONS

We report a novel FAM20A variant and, for the first time, the defective mineral composition and physical/mechanical properties of AI1G teeth.

Case report: Enamel renal syndrome: a case series from sub-Saharan Africa

Enamel Renal Syndrome (ERS) (OMIM # 204690) is a rare genetic condition characterised by hypoplastic amelogenesis imperfecta, failed tooth eruption, intra-pulpal calcifications, gingival enlargement and occasionally nephrocalcinosis. In this case series, we report on four unrelated patients with a confirmed molecular diagnosis of ERS (FAM20A pathogenic variants) from Sub-Saharan Africa. The pathognomonic oral profile of ERS was mostly fulfilled in these patients, with the notable addition of an odontoma in one patient. The cases presented a spectrum of phenotypic severity both dentally and systemically. One patient presented with nephrocalcinosis and abnormal kidney function, one had reduced kidney size with normal kidney function, and two had no renal abnormalities. Patients presenting with the oral profile of ERS should receive a prompt referral to a nephrologist and a geneticist. They should receive long-term management from a multidisciplinary medical and dental team.

Genotype-phenotype analysis of selective failure of tooth eruption-A systematic review

Tooth eruption is an important and unique biological process during craniofacial development. Both the genetic and environmental factors can interfere with this process. Here we aimed to find the failure pattern of tooth eruption among five genetic diseases. Both systematic review and meta-analysis were used to identify the genotype-phenotype associations of unerupted teeth. The meta-analysis was based on the characteristics of abnormal tooth eruption in 223 patients with the mutations in PTH1R, RUNX2, COL1A1/2, CLCN7, and FAM20A respectively. We found all the patients presented selective failure of tooth eruption (SFTE). Primary failure of eruption patients with PTH1R mutations showed primary or isolated SFTE1 in the first and second molars (59.3% and 52% respectively). RUNX2 related cleidocranial dysplasia usually had SFTE2 in canines and premolars, while COL1A1/2 related osteogenesis imperfecta mostly caused SFTE3 in the maxillary second molars (22.9%). In CLCN7 related osteopetrosis, the second molars and mandibular first molars were the most affected. While FAM20A related enamel renal syndrome most caused SFTE5 in the second molars (86.2%) and maxillary canines. In conclusion, the SFTE was the common characteristics of most genetic diseases with abnormal isolated or syndromic tooth eruption. The selective pattern of unerupted teeth was gene-dependent. Here we recommend SFTE to classify those genetic unerupted teeth and guide for precise molecular diagnosis and treatment.

The ABCs of the atypical Fam20 secretory pathway kinases

The study of extracellular phosphorylation was initiated in late 19th century when the secreted milk protein, casein, and egg-yolk protein, phosvitin, were shown to be phosphorylated. However, it took more than a century to identify Fam20C, which phosphorylates both casein and phosvitin under physiological conditions. This kinase, along with its family members Fam20A and Fam20B, defined a new family with altered amino acid sequences highly atypical from the canonical 540 kinases comprising the kinome. Fam20B is a glycan kinase that phosphorylates xylose residues and triggers peptidoglycan biosynthesis, a role conserved from sponges to human. The protein kinase, Fam20C, conserved from nematodes to humans, phosphorylates well over 100 substrates in the secretory pathway with overall functions postulated to encompass endoplasmic reticulum homeostasis, nutrition, cardiac function, coagulation, and biomineralization. The preferred phosphorylation motif of Fam20C is SxE/pS, and structural studies revealed that related member Fam20A allosterically activates Fam20C by forming a heterodimeric/tetrameric complex. Fam20A, a pseudokinase, is observed only in vertebrates. Loss-of-function genetic alterations in the Fam20 family lead to human diseases such as amelogenesis imperfecta, nephrocalcinosis, lethal and nonlethal forms of Raine syndrome with major skeletal defects, and altered phosphate homeostasis. Together, these three members of the Fam20 family modulate a diverse network of secretory pathway components playing crucial roles in health and disease. The overarching theme of this review is to highlight the progress that has been made in the emerging field of extracellular phosphorylation and the key roles secretory pathway kinases play in an ever-expanding number of cellular processes.

Enamel Renal Syndrome: A Systematic Review

The enamel renal syndrome (ERS) is a rare autosomal recessive disease that is associated with mutations in the FAM20A gene. The syndrome is characterized by impaired amelogenesis of the hypoplastic type and nephrocalcinosis, presenting with presence of thin or absence of enamel, late dental eruption, intrapulpal calcifications, bilateral nephrocalcinosis, and normal plasma calcium level. The objective is to characterize ERS by systematically literature reviewing, highlighting the main findings of the syndrome to increase knowledge about this condition in the health professionals. The study is a systematic review of the scientific literature, whose research was developed in the PubMed database in March 2018. A total of 69 articles were found. Two authors analyzed their abstracts and selected, according to the language and main subject, 30 articles to write this study. A total of 69 patients were cited in the studies and their data were analysed. There was gender equivalence and the ages ranged from 1 to 64 years old. There is a clear hereditary relation of the syndrome, since there was consanguinity in 18 cases, indicating a percentage of 26.08% and family history in 30 cases (43.47%). Laboratory changes vary greatly from patient to patient and may even remain unchanged. The relationship between the syndrome and the mutation in the FAM20A gene can be proven from the data, since all patients with ERS screened by the mutation were positive. With the advancement of the ERS studies, some associations with the syndrome are suspected, such as the presence of gingival fibromatosis, hearing loss, and hypertrichosis. Thus, it is noticed that the syndrome does not show a predilection for gender or age and there is a strong hereditary character, marked by the consanguinity and family history of the patients. The association with the FAM20A gene is reinforced, since the mutation was identified in all patients analyzed.

Two new families with enamel renal syndrome: A novel FAM20A gene mutation and review of literature

Enamel renal syndrome (ERS) or so-called amelogenesis imperfecta type IG is a very rare disorder characterized by the triad of amelogenesis imperfecta, gingival enlargement and nephrocalcinosis. It is caused by biallelic mutations in the FAM20A gene. Herein, we report two unrelated patients with ERS. Our patients presented with the characteristic features of the syndrome, and amelogenesis imperfecta and gingival hyperplasia were the main complaint. Strikingly, they both had long face, thick lips, notched upper central incisors, and thick alveolar ridge which have never been reported before in patients with ERS. Gingival biopsy showed psammomatous calcifications, and renal ultrasound revealed bilateral nephrocalcinosis in the two patients. Mutational analysis of the FAM20A gene identified two homozygous mutations including a novel one (c.915_918delCTTT, p.Phe305Leufs*76 and c.1219 + 3_1219+6delAGGT). Our data expand the phenotypic and mutational spectrum of FAM20A gene and reinforce the importance of kidney examination and follow up for all patients with amelogenesis imperfecta unless FAM20A mutations were ruled out.

Discovery of Selenocysteine as a Potential Nanomedicine Promotes Cartilage Regeneration With Enhanced Immune Response by Text Mining and Biomedical Databases

Background

Unlike bone tissue, little progress has been made regarding cartilage regeneration, and many challenges remain. Furthermore, the key roles of cartilage lesion caused by traumas, focal lesion, or articular overstress remain unclear. Traumatic injuries to the meniscus as well as its degeneration are important risk factors for long-term joint dysfunction, degenerative joint lesions, and knee osteoarthritis (OA) a chronic joint disease characterized by degeneration of articular cartilage and hyperosteogeny. Nearly 50% of the individuals with meniscus injuries develop OA over time. Due to the limited inherent self-repair capacity of cartilage lesion, the Biomaterial drug-nanomedicine is considered to be a promising alternative. Therefore, it is important to elucidate the gene potential regeneration mechanisms and discover novel precise medication, which are identified through this study to investigate their function and role in pathogenesis.

Methods

We downloaded the mRNA microarray statistics GSE117999, involving paired cartilage lesion tissue samples from 12 OA patients and 12 patients from a control group. First, we analyzed these statistics to recognize the differentially expressed genes (DEGs). We then exposed the gene ontology (GO) annotation and the Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analyses for these DEGs. Protein-protein interaction (PPI) networks were then constructed, from which we attained eight significant genes after a functional interaction analysis. Finally, we identified a potential nanomedicine attained from this assay set, using a wide range of inhibitor information archived in the Search Tool for the Retrieval of Interacting Genes (STRING) database.

Results

Sixty-six DEGs were identified with our standards for meaning (adjusted P-value < 0.01, |log2 - FC| ≥1.2). Furthermore, we identified eight hub genes and one potential nanomedicine - Selenocysteine based on these integrative data.

Conclusion

We identified eight hub genes that could work as prospective biomarkers for the diagnostic and biomaterial drug treatment of cartilage lesion, involving the novel genes CAMP, DEFA3, TOLLIP, HLA-DQA2, SLC38A6, SLC3A1, FAM20A, and ANO8. Meanwhile, these genes were mainly associated with immune response, immune mediator induction, and cell chemotaxis. Significant support is provided for obtaining a series of novel gene targets, and we identify potential mechanisms for cartilage regeneration and final nanomedicine immunotherapy in regenerative medicine.

Four novel mutations of FAM20A in amelogenesis imperfecta type IG and review of literature for its genotype and phenotype spectra

Amelogenesis imperfecta type IG (AI1G) is caused by mutations in FAM20A. Genotypic and phenotypic features of AI1G are diverse and their full spectra remain to be characterized. The aim of this study was to identify and summarize variants in FAM20A in a broad population of patients with AI1G. We identified a Thai female (Pt-1) and a Saudi male (Pt-2) affected with AI1G. Both had hypoplastic enamel, gingival hyperplasia, and intrapulpal calcification. Pt-1 also had rapidly progressive embedding of unerupted teeth, early eruption of permanent teeth, and spontaneous dental infection. Uniquely, Pt-2 had all permanent teeth erupted which was uncommon in AI1G patients. Whole exome sequencing (WES) identified that Pt-1 was heterozygous for FAM20A, c.758A > G (p.Tyr253Cys), inherited from her father. The mutation on maternal allele was not detected by WES. Pt-2 possessed compound heterozygous mutations, c.1248dupG (p.Phe417Valfs*7); c.1081C > T (p.Arg361Cys) in FAM20A. Array comparative genomic hybridization (aCGH), cDNA sequencing, and whole genome sequencing successfully identified 7531 bp deletion on Pt-1's maternal allele. This was the largest FAM20A deletion ever found. A review of all 70 patients from 50 independent families with AI1G (including two families in this study) showed that the penetrance of hypoplastic enamel and gingival hyperplasia was complete. Unerupted permanent teeth were found in all 70 patients except Pt-2. Exons 1 and 11 were mutation-prone. Most mutations were frameshift. Certain variants showed founder effect. To conclude, this study reviews and expands phenotypic and genotypic spectra of AI1G. A large deletion missed by WES can be detected by WGS. Hypoplastic enamel, gingival hyperplasia, and unerupted permanent teeth prompt genetic testing of FAM20A. Screening of nephrocalcinosis, early removal of embedded teeth, and monitoring of dental infection are recommended.